Calcite is a compound having a chemical formula of CaCO3, and exhibits multiform characteristics that are classified into three different minerals, that is, calcite, aragonite, and vaterite. However, in fact, calcite is widely and industrially used, and it has various shapes, such as, a spindle shape, a cubic form, a spherical form, and the like, depending on the synthesis method thereof. In addition, as the grain size becomes smaller and the whiteness is further increased, calcite is a material utilized more often for various functions, which increases product costs.
Calcite is generally referred to as calcium carbonate in the industrial field, and is sorted into heavy calcium carbonate and hard calcium carbonate. The heavy calcium carbonate is natural calcite, and also called stone powder. It is prepared by pulverizing limestone or crystalline calcite into several sizes using a pulverizer, and utilized as a general-purpose material such as fuel-gas desulfurization or the like. Meanwhile, in general, the hard calcium carbonate is chemically prepared by subjecting limestone to firing, hydrating, and synthesizing processes. It is very widely utilized in various industries since the quality of products is relatively easy to improve and the shape of the grain is controllable in accordance with usage thereof. In addition, calcium carbonate for food and drug is subjected to procedures of crystalline form treatment and surface treatment, impurity control, and the like, to control functions thereof in accordance with respective food and drug products, and quality requirement levels thereof are higher and higher-purity products are required as compared with general traditional products. For example, whiteness thereof is 96 to 97, which is at a high level, and an average grain size thereof has about several microns, which is minute. In addition, a restriction value on several heavy metals, particularly arsenic, is several ppm, which is very strict. This is currently used as an additive in foods, cosmetics, toothpaste, drugs, and the like.
Methods of synthesizing calcite in a large amount are classified into a carbon dioxide combination method, a lime soda method, a soda method, and the like. According to the carbon dioxide combination method, a limestone source is used or calcium hydroxide which is a reagent is used to prepare lime milk, and CO2 gas is blown thereinto (Equation 1). According to the lime soda method, lime milk or calcium hydroxide is reacted with sodium carbonate to prepare caustic soda, and here, calcite is yielded as a by-product (Equation 2). Meanwhile, according to the soda method, calcium chloride and sodium carbonate are reacted with each other to synthesize calcite (Equation 3). However, since the lime soda method and the soda method employ sodium carbonate and ammonium chloride, which are soluble salts, sufficient washing needs to be performed when calcium carbonate is collected, and grain sizes and grain shapes are difficult to control. Hence, in recent, they are never used.
Contrary to these, since the carbon dioxide combination method is relatively simple and leads to high purity, calcium carbonate is synthesized by this method, recently. This method has been known to easily control the grain shape thereof but not the grain size. Since, in particular, a growth rate of calcite is controlled by suppressing a dissolution rate of nucleus generated during a reaction procedure and diffusion of ions, a method of producing calcite for food, cosmetics, toothpaste, and drugs has recently been used by using a solvent, such as, ethanol, methanol, or the like, which has lower solubility and a lower dielectric constant than water.
The respective methods for synthesis are expressed as follows:Ca(OH)2+CO2═CaCO3+H2O  (Equation 1)Ca(OH)2+Na2CO3═CaCO3+2NaOH  (Equation 2)CaCl2+Na2CO3═CaCO3+2NaCl  (Equation 3)